Note: Descriptions are shown in the official language in which they were submitted.
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The prescnt invention relates to the construction of electric
motors and more par-ticularly but not exclusively to parallel flux induc-
tion motors and the rotors therefor.
As described in United States Patent No. 4,320,645 it is pos-
sible to form the rotor of a parallel flux induction motor from punched
metal strip, with the holes punched in the strip being aligned to form
radially extending slots on the core of the rotor.
The use of axial flux induction electric motors has generally
been limited to situations that do not require the motor to have a rela-
tively large starting or stalling torque, since it has been a problem
of axial flux electric motors that they do not have good low speed
torque characteristics.
It is an object of the present invention to overcome or sub-
stantially ameliorate the above disadvantages.
It has been found advantageous in the forming of rotors for
axial parallel flux induction motors, that the slots in the rotor
should be radially outwardly diverging, and more preferably that the
slots are divided by a projection having a generally constant widtll.
It has also been -foulld advantageous to h.lve the slots formed so th.lt
each slot consists of a Illai}l slot whicll brarlclles at a radicLlly out-
wardly spaced location from the inner peripheral surface of the rotor,
into one or more secondary slots. Still -further it has been fOUlld
advarltageous -that the slots at the location at WhiC}I they are exposed
to the end face of the rotor are defined by two metal projec-tions which
taper toward each othcr so as to inhibit the leakc-Lge of flux.
There is disclosecl herein a ro-tor core for an axial flux
induction electric machine, said ( ore being formed of
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metal strip wound about a central axis, said strip being punched
to have a first set of holes which are spaced longitudinally of
the strip so as to form a first se~ of radially extending slots
when located on the core, and wherein said slots have side walls
which diverge radially outwardly so that the angular area of the
slots increases radially outwardly.
There is further disclosed herein a rotor for an axial
flux electric motor, said rotor comprising a generally annular
core formed of metal strip punched with holes and wound about a
central axis, said holes being longitudinally spaced along the
strip so as to form radially extending slots in the core, flux
conduit rings extending along the radially outer and inner
longitudinal periphera] surfaces of said core, first flux
conductive bars extending through said slots and conductively
linking said rings, and further flux conductive bars also linking
said rings but joined thereto at a longitudinally spaced location
relative to the first conductive bars so that said core is
substantially located between the first and further bars, and
flux resistance means adapted to inhibit the passage of flux in
a loop extending around said core via said bars and rings.
There is still further disclosed herein a core for an
axial flux electric machine, said core being formed of metal
strip having holes punched therein and wound about a central axis,
said holes being spaced at longitudinally spaced locations so as
to form radially extending grooves in the core, said holes having
a first slot forming portion extending to the strip edge via s
slot neck portion, and wherein each neck portion is defined
between two projections which each taper so as to have a transverse
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width decreasing toward said neck portion.
A preferred form of the present invention will now be
described by way of example with reference to the accompanying
drawings, wherein:
Figure 1 is a schematic perspective view of a core of
a rotor of a parallel flux induction electric machine;
Figure 2 is a plan view of the core of a rotor for a
parallel flux induction electric machine;
Figure 3 is a segment of a metal strip which may be
wound to form the core of a rotor of a parallel flux induction
electric machine;
Figure 4 is a segment of a strip which may be wound to
form the core of a rotor for a parallel flux induction electric
machine;
Figure 5 is an end elevation of a rotor of an axial
flux induction electric motor;
Figure 6 is a schematic side elevation of the rotor of
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Figure ~ sectioned along the lines 6-6;
Figure 7 is an enlarged section view of a por-tion of the
rotor as illustrated in Figure 6;
E'igure 8 schema~.ically depicts a portion of the punched
strip used to form the core of the rotor of E'igure l; and
Figure 9 is an enlarged section view of a portion of the
rotor of Figure 5, and is taken on line 9-9 of Figure 5.
Firstly with reference to Figure 1, there is depicted
the core 10 which may be used to form the rotor of an axial
parallel f]ux induction electric motor~ which core is formed of
punched metal strip. The strip is wound about the axis 13 with
the holes in the punched strip being radially aligned so as to
form the slots 11. ~he slots 11 are separated by projections 12.
In this particular embodiment the slots 11, as more clearly seen
in insert A are formed so as to increase
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in cross-sectional area radially outwardly ~o that the cross-
sectional area of the slot adjacent the axis 13 i6 smaller
than the cross-section of the slot at a radially outwardly
spaced loc~tion. It is still further preerred that the
projections 12 have a substantially constant cross-section.
The slots 11 have a base surface 14, two side
surfaces 15 and a neck portion 16. ~ccordingly, in order for
the area of the slot 11 to increase, the side surfaces 15 of
each individual slot must diverge radially outwardly from the
axis 13. However, adjacent side surfaces lS of adjacent
slots are generally parallel so as to maintain the
cross-sectional area of the projections 12 generally constant.
Now with reference to Figure 2, there is depicted a
core 20 which may be used to form the rotor of an axial
parallel flux induction electric machine. The rotor 20 is
formed of punched metal strip which is wound about the
central axis of the core 20, with the holes punched in the
strip being radially aligned to form radially extending slots
as illustrated in the insert B. The slots consist of main
slots 21 which divide to form secondary slots 22 and 23.
In both the above described embodiments of Figures 1
and 2, the slots may be formed by the interaction of two
punches which co-operate with the feed rate of the strip to
form the desired slot cross section, e.g. as can more easily
be seen with reference to Figure 4, each slot 40 is formed by
the operation of two punches. As the feed rate of the strip
43 increases, one of the punches which initially did not
engage the strip, but pass through ~he aperture formed by the
first punch, begins to engage the strip, and therefore change
the cross-sectional area of the slot to be formed. As the
feed rate further increases the second punch forms a second slot 41.
In the formation of either core 10 or 20, the feed rate of the strip
being wound increases as the diameter of the core being formed in-
creases.
Now with reference to Fi.gure 3, there is iilustrated a
punched metal strip 30 which may be wound to form the core of the
rotor of an axial parallel flux induc-tion electric machine. Ihe strip
30 has punched holes 31 which have a neck aperture 32. Each aperture
32 is defined by two projecti.ons 33 which taper towards the aperture
32 so that the thickness of each projection in the plane of the strip
adjacent the aperture 32 is of the order of .020 to .030 inches. Addi-
tionallyg the extremities of the projections 33 may be spaced from .010
and .060 inches. The tapering of projections 33 increases the resist-
ance to the passage of flux across the aperture 32.
In Figures 5 to 9 there is depicted a rotor 50 having a cen-
tral passage 51 to receive a shaft, and a casi.ng 52 which has an outer
peripheral ring 54 and an inner ring 55 joined by radially extellding
flux conducting bars 53. The bars 53 are located on the axi.ally outer
end face o:f the roto:r wh:ilc on the ax:ia11y :i.nllcr t'acc 5(- thc r;ngs 54
and 55 are also joined by further radially cxtendillg flux con(luctive
bars 60. These further bars 60 are located in the radi..llly extcnding
slots in the core 57. Tlle casillg 52 encompasses a rotor core 57,
Wh:iCIl core 57 is folmed of ~ lchcd nletal strill 61 wound about tlle ax:is
of the rotor so -that the punched holes 62 ;n the strip 61 form radi-
ally extending grooves
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in the core adjaeent the face 56 through which bars 60 in that
faee extend. In practiee the field produeed by the stator and
which passes through the laminated structure of the core 57 and
the two sets of bars
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induces a current ln the oasing ~2 which roughly follows the
path indicated by the arrows 58. To increase the tor~ue of
this electric motor, the current induced in the casing 52 is
provided with a resistance by means of the groove 5~ machined
in the radially outer peripheral ring 54~
Now with reference also to Figure 8 wherein there is
depicted a portion of the strip which is wound to form the
core 57. As can be seen, the strip portion includes a
punched hole 58 which is aligned with other holes to form
radially extending grooves in the face 56 within which the
radially extending bars are formed. It is preferred that the
area of the hole 58 be equal to or less than the longitudinal
cross-sectional area of the outer peripheral ring 54.
Although the formation of the groove 59 influences
the starting torque of the motor, it should further be
appreciated that by forming the groove 59, the overall speed
and smoothness of operation of the motor is also altered. As
an example, as the size of the groove 59 is increased, the
speed of the motor is correspondingly decreased together with
the smoothness of operation of the motor. Accordingly the
motor characteristics can to some extent be predetermined by
the formation of a groove 5g of a particular configuration.
